This invention relates generally to voltage regulators and, more particularly, to voltage regulators used for controlling large solar cell arrays.
Solar cell arrays are widely used in providing power for spacecraft. The individual photovoltaic cells that make up a solar cell array are typically interconnected in various series and parallel networks to form power segments. The power segments are generally controlled by a voltage regulator in order to provide a constant supply voltage to the spacecraft load. The supply voltage must be regulated because the output voltage of each power segment varies as the amount of current drawn from that power segment varies and because of the inherently non-constant output characteristics of the individual solar cells. These non-constant output characteristics depend, for example, on the angle of disposition of the solar cells toward the radiant energy source, the degree of eclipse of the individual solar cells by spacecraft structures, and the temperature dependence of the solar cells.
Voltage regulators used to control solar cell arrays are typically classified as either a series type or a shunt type voltage regulator, depending upon whether the active element of the regulator is in series with the solar cell array or in parallel with the array. A shunt voltage regulator generally shorts the power segments or dissipates energy from the power segments through resistor or power transistor networks to maintain the supply voltage constant, while the series voltage regulator generally switches the power segments into and out of the output to maintain the supply voltage constant. The series voltage regulator is sometimes preferred because it does not require shorting out the power segments, as does the shunt voltage regulator. However, switch controllers of the prior art, which switch the power segments into and out of the output, frequently do not provide acceptable switching characteristics for the power segments. These switching characteristics include, for example, the number of switches required to control the power segments, the power requirements of each switch, the resolution provided by the switches, and the amount of control logic required to control the switches. Accordingly, there has been a need for an improved switch controller providing improved switching characteristics for the power segments of a solar cell array. The present invention clearly fulfills this need.